Oxides of titanium are known in the art. Among many others, Nawata et al (JP51081896) discloses use of TiO.sub.2 as a catalyst for production of high molecular weight polyesters. Shtokoreva et al (SU765290) cites the use of Ti.sub.n O.sub.2n-1 were n=3-7. The formula Ti.sub.n O.sub.2n-1 for these compositions can be equivalently rewritten as TiO.sub.x [x=(2n-1)/n] wherein x is between 5/3 (n=3) and 13/7 (n=7). Oxides of titanium have a variety of industrial applications.
The production of polyesters by polycondensation of diols and hydrocarbyl diacids is well known in the art, as described in the Encyclopeda of Polymer Science and Engineering, 2nd ed, volume 12, John Wiley and Sons, New York (1988). The most common polyester so produced is poly(ethylene terephthalate) (hereinafter referred to as PET). PET is generally formed into a low molecular weight prepolymer by transesterification of dimethyl terephthalate or esterification of terephthalic acid with ethylene glycol to form a bis(hydroxyalkyl)ester which is subsequently subject to polycondensation by transesterification to form a high molecular weight polyester. Because the transesterification is an inherently slow reaction, which requires holding the reactants at elevated temperatures for protracted periods with concomitant thermal degradation, the polycondensation step is generally catalyzed.
It is, however, highly desirable to produce a polyester with usefully high molecular weight and low yellowness at as high a rate as possible. Yellowness in polyesters is normally a result of polymer degradation and side reactions occurring during either polymerization or down-stream processing. Thus yellowness in the polymer as synthesized is indicative not only of the quality of the polymer so-produced, but also of further processibility of the polymer into fabricated forms in color-sensitive applications such as fibers, films, and certain molded parts. While many catalysts for production of high molecular weight polyesters are known, they suffer from a deficiency in either rate of conversion, ease of use, or quality of the product formed therewith.
Antimony-containing compounds are currently in widespread commercial use as catalysts which provide a desirable combination of high reaction rate and low color. However, there is considerable inducement to find a substitute for antimony because of the expense and difficulty of handling the known-to-be toxic antimony in an environmentally responsible manner.